568 
PHYSICAL OCEAN OGKAPH Y OF THE GULF OF MAINE 
The spacial distribution of temperature in May may be illustrated in a more 
connected way by three west-east profiles of the gulf — the first for April 28, 1919 
(fig. 35), the second for May 4 to 7, 1915 (fig. 36), and the third for May 29 to 30, 
1919 (fig. 37). 
The first of these is interesting chiefly as it outlines the extension of the cold 
Nova Scotian current into the eastern side of the gulf, indenting like a shelf into the 
warmer water of the basin (isotherm for 4°, fig. 35). Water almost equally cold, 
washing the slope of Cape Cod at 60 to 120 meters in the opposite side of the profile, 
is reminiscent of the previous winter’s cooling in situ; and the definite separation of 
these two cold masses by slightly higher temperatures in the central part of the basin 
deserves emphasis. Unfortunately no readings were taken deep enough in the basin 
to show what relationship the temperature of the bottom stratum bore to that of 
the mid depths at the time. So far as they go, however, they point to a homogeneous 
state at depths greater than 100 meters. 
Although the May profile for 1915 (fig. 36) was run only a week later in date, 
the presence of a lenticular mass of 5° to 6° water over the western part of the basin, 
with maximum thickness of about 50 meters, illustrates a considerable advance in the 
seasonal cycle, reflecting the penetration of solar heat downward from the surface 
into the underlying water. Below it the cold coastal band that skirts the western 
side of the gulf earlier in the spring (the product of local chilling) is still represented 
at the mouth of Massachusetts Bay by temperatures of 3.5° to 4° at depths greater 
than 20 meters. 
Whether the cold water of Nova Scotian origin in the eastern side of the gulf 
assumed a shelflike outline earlier in that particular spring, as it certainly did in 
1919, is not known. If so, its tip had been eaten away by mixture with the sur- 
rounding water until its limiting isotherm (4°) had come to assume the more nearly 
vertical course shown on the profile (fig. 36). In actual temperature, however, this 
cold water mass was very nearly the same in 1915 as the ice patrol found it in 1919 f 
one of the many illustrations that might be cited of the surprising constancy of the 
gulf in temperature from year to year. The presence of appreciably warmer 
(4° to 5°) water below it in both these years illustrates how strictly the inflow past 
Cape Sable into the gulf is confined to the upper stratum above the 100 to 120 meter 
level, a phenomenon resulting from the distribution of density in this side of the gulf 
(p. 946). As a consequence, the surface is the coldest level there in May, or at least 
the lowest readings will be had only a few meters down. 
Figure 37 illustrates still a later stage in the thermal cycle, the Nova Scotian 
current having slackened and the two cold water masses that hug the two sides of 
the gulf earlier in the season having merged into the general stratum of minimum 
temperature (4° to 5°) at the 50 to 120 meter level. Vernal warming is illustrated 
further on this profile by arise in the temperature of the upper 10 meters from about 
5° at the end of April (5° to 6° on May 4 to 6, 1915) to 8° to 9°. In the deeps of 
the gulf a rise in temperature from about 4.5° to 5.6° to 6° during the preceding four 
weeks (cf. fig. 37 with fig. 35) is evidence of a considerable movement of slope water 
through the Eastern Channel into the gulf during the interval. However, the nearly 
horizontal course of the isotherm for 5 degrees across the basin on May 28 (fig. 37) , 
